My Dometic RV fridge is sucking my batteries dry and I can't determine why?!

[Petenebraska]

My wife and I now live fulltime in our 34' fifth wheel. We are currently in TX. In October, we went to Hawaii for a month and while we were there, I contracted with a company in Idaho to install a solar system. I now have 18 - 100w panels, a 6000w inverter/charge controller, 2 100ah/ 48v LiFePo rack batteries and a battery monitor (SOC reader). I started having troubles with it immediately but was assured that it was an exceptionally robust system and would accommodate our lifestyle of travelling and following the weather (not running the A/C units "all the time".) Through many conversations with the installer (who is great, by the way) we are leaning in the direction that the Dometic RV fridge (absorption style) is sucking too much juice. It pulls 400 - 500w for most of the day. It's very rarely pulling less than 350w. Well, that doesn't pencil out and my installer says that his research suggests that RV fridges are supposed to be MORE efficient than residential, so he can't imagine how it's pulling so much.
When the system was installed, the installer decided to leave the whole 12v system (12v lead acid battery, 12v charger/converter, wiring, fuses, etc) intact and just bypass all of that and wire directly from the new 6000w inverter to the breaker panel. Initially, I thought that sounded like a good idea, but my continuing problems make me think that wasn't the best design?
Does anyone have any suggestions about A.) Should we have pulled the existing 12v system out of the trailer prior to installing the new system and installing a DC to DC converter?
B.)Have you ever heard of an RV fridge pulling this much juice and do you know of a "fix". I'm considering buying a new, small residential fridge to replace this one and just plug into the 110v outlet in the fridge cabinet and letting the 48v batteries handle it without the added complications of the 12v DC and propane inputs.

Thanks!
Pete

 

[John Frum]

RV fridges are often modal.
There is often a switch to run...
1. primarily off of propane with very minimal 12 volt dc draw.
2. purely off of the 12 volt dc distribution panel
3. purely off of 120VAC

Is your fridge modal?
If yes, which mode is it in?

 

[John Frum]

For a test turn your fridge off and see if the draw goes to zero.
Report back please.

 

[Petenebraska]

Yes, Modal.
Two settings: AC or gas. There are two buttons on the front panel. One is the pwr button (on/off) and the other is "Auto" which toggles the setting from AC to gas. When "Auto" is on, the fridge seems to recognize if 120 pwr is coming in so it enables that function. If I turn the "Auto" button off, the fridge switches to gas and runs off of propane.

 

[Petenebraska]

For a test turn your fridge off and see if the draw goes to zero.
Report back please.

It does not go all the way to zero (I have Starlink, some laptops, phones, LED lights etc.) running in the background.

 

[400bird]

Sounds like your absorption fridge is running on electric only mode.
I've heard they burn tons of energy in electric mode and are far less efficient than a residential fridge with a compressor.

 

[John Frum]

It does not go all the way to zero (I have Starlink, some laptops, phones, LED lights etc.) running in the background.

The starlink uses a lot of juice.
From memory about 100Watts.

 

[Petenebraska]

Sounds like your absorption fridge is running on electric only mode.
I've heard they burn tons of energy in electric mode and are far less efficient than a residential fridge with a compressor.

I"m sure it's running on electric only. And I read this article https://www.beginningfromthismorning.com/refrigerator/ suggesting that you are right about it burning tons of energy. My installer, though, is sure that it's supposed to be more efficient. We're trying to exhaust all possible options before throwing in the towel and buying a new fridge.

 

[John Frum]

Yes, Modal.
Two settings: AC or gas. There are two buttons on the front panel. One is the pwr button (on/off) and the other is "Auto" which toggles the setting from AC to gas. When "Auto" is on, the fridge seems to recognize if 120 pwr is coming in so it enables that function. If I turn the "Auto" button off, the fridge switches to gas and runs off of propane.

How much power does it draw when its running off propane?

I suspect your system is set up so that your inverter effiency and your ac/dc converter efficiency are compounded.

Inverter is ~85% efficient at converting dc to ac and the converter is ~75% efficient at converting dc to ac.
That means your overall efficiency for dc 12 volts is ~63.75%.
That means for every 12 volt dc watt you draw you draw ~1.57 watts in the 48 volt dc domain.

 

[Petenebraska]

The starlink uses a lot of juice.
From memory about 100Watts.

Well, we've tested that before (this has been a months long process) and we determined that its only pulling 30 - 50?! But, even if it IS pulling 100, should the fridge be continuously pulling 350 - 450 all day long??

 

[Petenebraska]

How much power does it draw when its running off propane?

I suspect your system is set up so that your inverter effiency and your ac/dc converter efficiency are compounded.

Inverter is ~85% efficient at converting dc to ac and the converter is ~75% efficient at converting dc to ac.
That means your overall efficiency for dc 12 volts is ~63.75%.
That means for every 12 volt dc watt you draw you draw ~1.57 watts in the 48 volt dc domain.

This is what I'm thinking too! The conversion is getting me! Do you think it would be wiser to do away with the original 12v battery and inverter and install a DC to DC converter to power the 12v system in the camper?

 

[John Frum]

But, even if it IS pulling 100, should the fridge be continuously pulling 350 - 450 all day long??

RV fridges have a reputation for being quite inefficient when running on AC.
The engineering department is not paying for the juice and when they were designed it was assumed that the RV owner was getting flat rate power from the RV park.
So AC efficiency would not be a priority.

 

[John Frum]

This is what I'm thinking too! The conversion is getting me! Do you think it would be wiser to do away with the original 12v battery and inverter and install a DC to DC converter to power the 12v system in the camper?

You have 48 volt batteries.
You should have a 48 volt inverter charger.
If the inverter is running off of the converter that would be a shit show.
Please confirm your dc to ac inverter is 48 volts.

 

[Petenebraska]

RV fridges have a reputation for being quite inefficient when running on AC.
The engineering department is not paying for the juice and when they were designed it was assumed that the RV owner was getting flat rate power from the RV park.
So AC efficiency would not be a priority.

Well, crud!

What would your suggestion be to rectify this situation? I've asked the installer about buying a new fridge. I've asked about installing another battery for more capacity. I've asked about eliminating the 12v battery system. I'm not sure what other direction to turn.

 

[time2roll]

Run the fridge on propane only. Otherwise a compressor fridge is needed.

 

[John Frum]

Well, crud!

Are you saying its a 12 volt inverter?
If yes please show me the 48>12 dc2dc converter.
That should be interesting .

 

[Petenebraska]

You have 48 volt batteries.
You should have a 48 volt inverter charger.
If the inverter is running off of the converter that would be a shit show.
Please confirm your dc to ac inverter is 48 volts.

I have both. The trailer has the original 12v inverter and battery and then a 48v system was installed "around" it. The installer left the 12v in place then connected the 48v to the breaker panel to just leave as much of the original system in tact.

 

[Petenebraska]

Run the fridge on propane only. Otherwise a compressor fridge is needed.

Check one in the compressor fridge category! This is the way I'm leaning... Thanks.

 

[John Frum]

I have both. The trailer has the original 12v inverter and battery and then a 48v system was installed "around" it. The installer left the 12v in place then connected the 48v to the breaker panel to just leave as much of the original system in tact.

You can't have both inverters connected to the ac distribution panel.
Please turn off the 12 volt inverter.
Do you have a dedicated ac2dc converter?

 

[Tecnodave]

Adsorption referigeration is incredibly inefficient. Steady state draw on AC or DC is about 300 watts. It is not compressor driven, it has electrical heating elements to evaporate the ammonia.

I am using Grape Solar referigerators that fit in the space of the original adsorption referigeration. It draws 42 watts with a 20% (.2-.3 kw/ day) run time verses 300 watts continously (7.2 kwh/day) of the Norcold adsorption unit. The units are 10 to 15 volts (basically 12 volts) or 20 to 30 volts (basically 24 volts) or 90 to 135 volts AC. It auto detects incoming voltage. There are two separate power cords for AC and DC. Though not really meant for RV,s they do well in that enviroment.

Grape Solar has exited the business but there are others marketing DC powered fridges